The present invention generally relates to an electric vehicle having a regenerative braking system used to recover energy for an on-board rechargeable power supply. More particularly, the invention relates to rider controlled actuating devices for the regenerative braking system.
As exacerbation of air pollution by large numbers of internal combustion vehicles has become a significant concern in large cities, efforts are being made worldwide to provide efficient electric powered vehicles which do not discharge pollutant emissions. Large cities in developing countries which include high concentrations of scooters powered by two stroke engines are particularly affected by vehicle pollution. These two stroke scooters produce large quantities of pollutants and significant noise. Electric powered scooters, on the other hand, offer a means of transportation that emits substantially no pollutants and produces very little noise.
Electric scooters typically have a bank of batteries which provide power to a drive motor. These batteries must be recharged from time to time. This is typically done by plugging the batteries into an AC power outlet for a period of time to restore the depleted energy. However, to improve the autonomy of a vehicle, there is reason to place battery charging units and battery energy conserving units permanently onboard electric scooters. In particular, regenerative braking systems can be used to transform kinetic energy of the vehicle back into electrical energy to help recharge the vehicle batteries during the braking mode. This provides a braking system that is more energy efficient, and simpler, than that provided by friction brakes.
One system known for controlling regenerative braking in an electric vehicle is disclosed in U.S. Pat. No. 5,644,202 which teaches a regenerative braking control system that is capable of individually controlling braking force and recharging energy. The braking force and recharging energy are set based on the charge of the battery and motor speed to obtain an optimal braking force and an optimal recharging current. The system teaches establishing an optimal braking force and then providing a recharging current that is optimized so that the recharging current is increased when the battery voltage is low and is decreased when the battery voltage is high.
Another regenerative braking system for an electric vehicle is known from U.S. Pat. No. 5,615,933 which discloses a four wheeled vehicle having an electric propulsion motor, a regenerative brake control, and a friction anti-lock brake system (ABS) in which regenerative braking may be blended with friction braking when anti-lock braking is not activated. Regenerative braking, however, is ramped down or immediately removed when antilock braking is activated.
Similarly, U.S. Pat. No. 5,472,265 discloses an antilock braking apparatus having a regenerative braking part, a second braking part, an antilock brake system part, and a braking control part in which the antilock brake system part performs an ABS control process to control a braking force produced by either the regenerative braking part or the second braking part on the wheels. The braking control part changes the braking force produced by the other braking part on the wheels to equal zero when the antilock brake system part has started performing an ABS control process.
The invention is related to a wheeled vehicle with a regenerative braking system. The preferred vehicle has least two wheels and carries one or more rechargeable batteries or another electric energy storage device. The preferred regenerative braking system includes a brake control configured for movement by a user over a movement range that includes first and second subranges. A regenerative device is associated with the batteries and at least one of the wheels for generating an electrical current by decelerating the wheel. Additionally, a processor is connected to the brake control and to the battery such that when the brake control is subjected to a first movement, preferably by positioning it in the first subrange, the processor causes the regenerative device to decelerate the vehicle and charge the batteries with the current produced. The processor is preferably also configured for activating another operation of the vehicle when the brake control is subjected to a second movement, preferably by positioning it in the second subrange. In one embodiment, the first movement is in a first direction, and the second movement is at least of a predetermined minimum rate and in a second direction opposite from the first direction.
An electric motor is operatively connected to at least one of the wheels to drive it, and a motor controller connects the batteries to the electric motor to power the motor. The preferred brake control includes a twist grip throttle, with the processor having an electrical connection to the motor controller and for causing the motor to accelerate or power the wheel when the brake control is positioned in the second subrange. In one embodiment, the processor also activates another braking system for decelerating the vehicle when the brake control is positioned in the second subrange. The first subrange preferably comprises less than about 25 percent of the range, and more preferably less than about 15 percent. The preferred brake control is resiliently biased towards a resting position between the first and second subranges.
In a preferred embodiment, the invention provides a regenerative braking system for an electric vehicle having front and rear wheels, and includes a drive wheel, an actuating device, a regenerative braking control circuit, and a power electronics circuit. The regenerative braking control circuit includes a transducer, such as a potentiometer or digital encoder or the like, a process sensor, and a microprocessor. The power electronics circuit includes a rechargeable electric power source, an electric motor, and a motor controller. The actuating device is coupled to the transducer. The transducer and process sensors signal the microprocessor which applies an algorithm to the signals and produces an output signal to the motor controller for regulating a regenerative braking torque to the drive wheel. The algorithm includes a subroutine for preventing lock-up of the drive wheel. In one embodiment, the regenerative braking system is independent of a vehicle friction brake system. In another embodiment, the regenerative braking system cooperates with a friction brake system.
The braking system applies a regenerative braking torque to the drive wheel when the transducer signals a regenerative braking command, and the process sensors signal a drive wheel velocity greater than zero. Preferably, the braking torque increases with an increase in the transducer signal as controlled by the operator, and the subroutine adjusts the braking torque when an anti-lock trigger is activated. In essence, during the regenerative braking mode, the motor act as a generator supplying current to the battery which loads down the generator, thereby causing a braking action.
In an illustrative embodiment of the invention, the process sensors comprise a rear wheel velocity sensor and a front wheel velocity sensor. The trigger activates when the front and rear wheel speeds differ by a set value. In one example, the set limit is about 5 percent. The adjustment in regenerative braking torque is related to the difference between the front and rear wheel speeds. For example, the regenerative braking torque may be determined by the antilock subroutine unless the regenerative braking torque signaled by the transducer is less than the adjusted regenerative braking torque determined by the subroutine, or the difference between the front and rear wheel speeds exceeds a predetermined limit.
Preferably, the actuating device is mechanically movable over a range of motion and is capable of being controllably positioned by a vehicle rider. In an exemplary embodiment, the actuating device is operably configured to cooperate with the transducer to signal the microprocessor. The mechanical position of the actuating device determines the transducer signal. In one embodiment, the range of motion comprises a plurality of subranges, and movement over a first subrange demands regenerative braking and movement over a second subrange demands friction braking. In one example, the first subrange comprises a displacement within about the first 25 percent of the total range, more preferably within about the first 10%, and the second subrange comprises a displacement within the remaining range of motion.
Typically, the vehicle may have a handle bar having first and second ends. In one embodiment, the actuating device is a hand brake comprising a lever located on the first or second end of the handle bar. In another embodiment, the actuating device comprises a thumb lever mounted to the handle bar and is located below the first or second end. In another embodiment, the actuating device comprises a twist-grip throttle located on one end of the handle bar for controllably accelerating or regeneratively braking the vehicle. In yet another embodiment, the actuating device comprises a foot pedal located on a side of the vehicle, preferably as well as for operating the vehicle in reverse at low speeds.
In one embodiment, the throttle is biased toward a neutral resting position and is bi-directional, being rotatable about the handle in first and second directions. Rotation of the twist-grip throttle from the neutral position in the first direction demands vehicle acceleration, and rotation of the twist-grip throttle from the neutral position in the second direction demands regenerative braking.
In another embodiment, rotation of the twist-grip throttle from the neutral position in the second direction comprises a plurality of subranges, and movement over a first subrange demands regenerative braking and movement over a second subrange demands a different form of braking. In one example, the first subrange comprises a rotational displacement within about the first 25 percent of the range, and the second subrange comprises a displacement within the remaining range of motion.
In another embodiment, the twist-grip throttle is biased toward a neutral resting position and is capable of rotating from the resting position about the handle in a first direction. Rotation of the twist-grip throttle from the resting position over a first subrange demands regenerative braking, and rotation of the throttle over a second subrange demands vehicle acceleration. In one example, the first subrange comprises a rotational displacement within about the first 25 percent of the range, more preferably within about the first 15% of the range, and the second subrange comprises a displacement within the remaining range of motion.
The present invention also relates to an operator-controlled twist-grip throttle for an electric vehicle that controls a regenerative braking system. The twist-grip throttle includes a handle, or grip, having a longitudinal axis, first and second ends, and a sector gear located at a first end of the handle and fixed thereto against relative rotation. A transducer operably designed and configured to translate a rotational position of an input gear into an output signal is also associated with, and perhaps even included within, the twist-grip throttle. The transducer may be a potentiometer or a digital encoder, or the like.
Preferably, the sector gear is operably designed and configured to mate with the input gear, and rotation of the twist-grip throttle about the handle causes the sector gear to controllably change the relative position of the input gear and signal a demand for vehicle acceleration or regenerative braking. The transducer is in electronic communication with a microprocessor and is also connected to a power lead and a ground.
In one embodiment, the handle further comprises first and second recesses within the first end of the handle which are spaced from one another and are operably designed and configured to cooperate with a bidirectional resilient member attached to a mounting part to bias the twist-grip throttle in a neutral position.